Atomic Mass of Silver

based on 6 ratings
Author: Cy Ashley Webb

Grade Level: 8th - 10th; Type: Chemistry


The goal of this experiment is to learn about atomic mass, atomic number, relative atomic mass and how different isotopes of an element affect the relative atomic mass.

Research Questions:

  • What is atomic mass? How does it differ from relative atomic mass?
  • How can atomic mass be calculated?
  • How does atomic mass differ from atomic weight?
  • Is it possible for an element to have different atomic masses? Why?
  • What percent of uranium is radioactive?

Students often confuse atomic number, atomic mass, atomic weight and relative atomic mass. The following definitions may be helpful:

Atomic number is the number of protons in an element. This number is always the same for every atom of a particular element; it is a fundamental property of the element.  

Atomic mass is the total mass of protons, electrons and neutrons in an atom. Unlike atomic number, atomic mass is not a fundamental property of an element; rather, it is a fundamental property of a particular isotope.

An isotope is a particular form of an element. While all isotopes have the same number of protons, the number of neutrons can vary. For example, hydrogen has three isotopes: protium (with 0 neutrons), deuterium (with 1 neutron) and tritium (with 3 neutrons).  

Atomic weight is the ratio of the average mass of atoms of a particular element to 1/12 the mass of an atom of carbon-12. While different samples of a particular element may have slightly different atomic weights, this number is sufficiently important that it appears on the periodic chart.

Relative atomic mass is a synonym for atomic weight. It represents the average of the mass of all isotopes weighted by the abundance of each isotope. 


This “paper-and-pen” experiment does not require setting up any special apparatus. All that is needed is a periodic table.

Experimental Procedure:

Relative Atomic Mass of Silver

  1. The formula for relative atomic mass is the relative abundance over 100 divided by the isotope number. This can be expressed as:

(A/100 • a) + (B/100 • b) + (C/100 • c)…. = relative atomic mass

A, B, C stand for different relative abundances of isotope numbers a, b and c.

Silver has two isotopes, silver 107 and silver 109. The relative abundance of these is 51.84 % and 48.16 % respectively.
Calculate the relative atomic mass of silver.

Relative Atomic Mass of Uranium

  1. Uranium has three isotopes: U 234, U235 and U238. The relative abundance of these is 0.01%, 0.71% and 99.27 % respectively. Use this information to calculate the relative atomic mass of uranium. 

Relative Atomic Mass of Barium

  1. There are seven different isotopes of barium. Doing on-line research, find out what these are and their relative abundance. Use this information to calculate the relative atomic mass of barium.

Terms/Concepts:  Atomic number; Atomic mass; Atomic weight; Isotope; Relative atomic mass


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